The present invention describes the production of shaped bodies, especially man-made boards, using agricultural waste products.
The processes for producing man-board products from cellulosic fibers, especially wood chips or other low quality forest or wood residues are well known to those skilled in the art. However, wood by-products are becoming more expensive and difficult to obtain as the natural wood resources are depleted. Furthermore, particleboards produced from wood residues have been shown to be highly flammable. Therefore, it is highly desirable to replace the wood residues in the board production process with more easily obtainable agricultural waste products that are less expensive, less flammable and can make boards of equal or superior properties.
The production of wood-like particleboard from agricultural waste products such as straws and grasses has been the subject of several prior patents (U.S. Pat. No. 5,656,129, U.S. Pat. No. 5,779,955 and U.S. Pat. No. 5,554,330). These existing processes produce fiberboard that has been shown to have a wide range of variability in its properties due to the range of variability in the natural products. In all of the earlier patents it was assumed that the same amount of binder could be used regardless of the properties of the substrate material. It has also been assumed that the processing conditions described are valid for a wide range of particle sizes, ages of material, and material compositions.
Wheat straw, an abundant and renewable resource, has a number of inherent disadvantages as compared to wood chips and other natural wood residues. Nonetheless, wheat straw has been used in processes that typically rely on wood products. U.S. Pat. No. 5,656,129 provided a method of refining wheat straw to produce fiberboard. However the method required long lengths of straw (2 to 4 inches) and high refining energy of 500 kWh to 1500 kWh per ton.
PARTICLE BOARD shall mean engineered shaped composites, including but not limited to fiberboard products of varying densities and mat boards.
AGRICULTURAL WASTE shall mean cellulosic materials, including but not limited to straws, grasses, rice straw, palm waste, wheat straw, plant waste or paper mill waste. Those of ordinary skill in the art will understand that agricultural waste can also be termed biomass.
The objective of this instant invention is to overcome some of the existing problems. It was found when materials of higher cellulose and hemicellulose content and lower silica content are selected, materials that have not undergone partial degradation, the processing conditions for high quality board turn out to be surprisingly different than those earlier described.
The possible combinations of various material properties and processing conditions are very large. It is the objective of this instant invention to incorporate the optimum processing parameters relative to the composition of the agricultural material being used. The key features of this instant invention are:
1. Determination of the general chemical composition of the substrate, specifically the cellulose and hemicellulose content, ash content (silica and other inorganics), water content and lignin content,
2. Selection of substrate materials based on the chemical composition,
3. Use of low energy refining to maintain structural integrity in the fiber,
4. Selection of the appropriate particle size to feed the refining process to produce good fiber substrate,
5. And utilization of the minimal amount of resin to achieve the desired bonding.